Jump to when cars arrived on the island. The residents took measures like limiting the number of cars; segregating streets for car traffic, etc. All this was intended to prevent car accidents. These  preventive measures are examples of primary prevention.

The important difference between the previous scenario (and the present) is the presence of cars. [In the last post, the cars were described as a risk factor.]

The occurrence of a car accident would be an outcome.

Till now the outcome (car accident) has not occurred. However, preventive measures have been instituted:(i) in the absence of risk factor (primordial prevention); and (ii) in the presence of risk factor (primary prevention).